We have continued our studies of the production of plasminogen activator by ovarian granulosa cells. In vivo this enzyme is produced in preovulatory follicles as ovulation approaches. In vitro the cells are stimulated to/ synthesize and secrete plasminogen activator by FSH, cAMP and A, B, and E prostaglandins. The in vitro response has proved useful as a very sensitive bioassay for FSH. The results obtained by this method can be compared directly with those of the Steelman Pohley bioassay for FSH. We have also demonstrated that hormonal stimulation can be communicated by a cell contact dependent mechanism to and from granulosa cells. Given the widespread existance of intercellular communication between these cells in situ, it would appear that this process is important in granulosa cell physiology. Finally, we have demonstrated the existance of cell-to-cell communication between the cumulus cells and the oocyte. These studies have revealed that communication between these cells is interrupted as ovulation approaches. The breakdown in communication occurs with the same time course as the the appearance of plasminogen activator. Furthermore, the apparent channels for communication between the oocyte and cumulus cells distintegrate during the same time period. In the coming year we will explore the role of communication, and its interruption, in oocyte maturation.